Structural, Civil, Architectural 1

[AppliedEx]

I'm in excavation. I use CADs to program our machines via GPS. Most of the time getting cads with/without a release is not a problem. However on one job we are running into a structural engineer and architect who are claiming structural cads can't be relied upon for measurement for dimensions.

Is there a basis for this? Is there a best practices handbook or something I can point to one way or the other to help me understand? For me it makes no sense because everyone moved away from paper/pencil/drawing boards a while ago and to the preciseness of AutoCad (or similar). But now I feel like I'm going back to the drawing board. Literally. GPS/CADs can help reduce errors, reducing staking/surveying costs, and increase speed of construction. Paper won't ever be eliminated but it's as if it is playing a bigger role than necessary.

Thank you for your time.

 

[Guastavino]

1. Who are you going to sue when you put in a point that was from their drawing?

2. Liability, liability, liability

3. Also, many architects and engineers use "nominal" dimensions. IE, an 8" CMU wall is really 7.625", but we might draw it as 8".

4. Lastly, many engineers never enter CAD. They simply rely on printed drawings that they mark-up etc. They know what's on print, but they don't know what's their electronically.

As one last aside. I typically don't let fabricators use my drawings for shop drawings either. They need to rework the dimensions and it's a good way for them to check things out.

 

[sponton]

Agree with njlutzwe, it makes a pain in the butt checking shop drawings but at least you know that it helps spot mistakes that could have gone unnoticed by both engineers and architects.

 

[thaidavid40]

Developing shop drawings from the contract drawings has been, and continues to be, an important part of the building process. It engages the contractor deeply in the details of the construction, so that he has a better understanding of the requirements to be met, and the conditions surrounding the meeting of those requirements. And as @njlutzwe said, it provides an additional check against errors and omissions. For that reason, our company does not offer our CAD drawings to fabricators for their unrestricted use. If a client compels us to do so, then we always release them with a disclaimer that they do not represent a perfect work product, and the end user shall not rely on them, and he is totally responsible for the end results of their work products.
Dave

Thaidavid

 

[EngineeringEric]

I am sure many people have hardwired a dimension before. Say the architect shifts the size of a canopy by 1"... In CAD during the 11th hour chasing the half inch is difficult and sometimes overwriting that one dimension is easier. Now if someone built it on the CAD dimension vs the sealed dimension dimension then who is to blame?

Sorry, I am paid to provide sealed construction documents. Not CAD (excluding BIM Models)

 

[racookpe1978]

CAD, particularly well-structured and accurate 3D CAD, is a good system in well-defined environments: Best for mechanical and machining and assembly of well-defined and very accurate assembly and motion-simulated of known-tolerance parts.

But would you build a 3D CAD model of a rebuild of an old multi-story steel structure with wood-and-drywall (or steel 2x4 and arch detailed) office interiors?

Your basic model of "where the walls are" starts off inaccurate because it wasn't built-to-drawings (exactly) in the first palce, and the settlement and movement and adjusts since then in AC, electrical, and mechanical services were never detailed in the originals: They were laid out, but fab'ed in-place.

Civil-steel details, arch details (windows, roof edges, watertight seals, repeated fittings, etc), HVAC, steel 3D CAD, and even well-dimensioned 2D CAD dwgs are essential, but they are not a CAD-CAM machinable assembly dwg. You'll need as-found field dimensions.

 

[SteelPE]

I had a thread about this 1.5 years ago. However, the architect was refusing to send me the drawings for my design purposes as the dimensions on their plans might not be correct. I refused to sign and I never received the CAD architectural drawings.

How about his, I have a building on my desk right now that is 1/2 conventional 1/2 specialty structure. The specialty structure is built using metric units, the conventional structure is built using imperial units (as that is the way construction is done here). Well, after going around about a bust in the specialty structures dimensions (happened during conversion) I gave up and erased all dimensions on my plans relating to their structure. So while the drawings may be off slightly, the GC is going to have to figure out what to do in the field.

 

[JStructsteel]

Well, all aside, ANYONE that is using a electronic drawing package should draw everything structural to scale in plan. If its CMU, draw it at 7.625", I understand you will use a line to show centerline of the beam, etc, but draw it to the correct length.

As for getting GPS coordinates, you should redraw it anyway to make sure its correct.

Like stated above, some dont draw to scale, but the printed version might be correct....example, a span is 25', in cad it measures 24'-7", but the dimension was fat fingered to read 25'-0". Right on paper, wrong in CAD.

 

[Brad805]

There are two camps in this type of thread. We have provided civil data for GPS controlled equipment, passed 3d BIM models to steel detailers, and believe in drawing elements as close to correct as we know. Admittedly, we have a fairly well defined group of tradesman we work with, and rarely do we ever work directly for the Architect. The guys on site are not math guys, and we are kidding ourselves if we think they will check and find our minor mistakes. As far as your fundamental question is concerned, it comes down to the contract between the owner and professional. To demand this information it would need to be defined in the contract. We have clients that stipulate that we provide CAD files in the contract. If it is not defined in the contract it is hit or miss if the professionals will provide the data. That said, 10minutes with inkscape or some other program and I can convert any raster .pdf file into CAD. That will not work for GPS equipment that needs 3d coordinates, but it is a start.

 

[JStephen]

Their response may be based on past negative experiences doing exactly the same thing.
Or, they may be aware of some assumed contours or similar issues where the CAD files don't correspond to reality.
In my work, I always draw things to scale.
Unless, that is, I'm making one drawing into another drawing, and it's quicker and easier to just manually overwrite the numbers than it is to start stretching and adjusting everything.
I do see drawing files where the size of items is adjusted in model space to change the apparent size on the paper.

 

[AppliedEx]

Thank you everyone that so far has taken the time to respond. Here was the problem. We use Trimble GPS (same stuff as the surveyors)to program our machines (excavators, dozers etc.). We take civil drawings and overlay the structural over the top. Never really had a problem until now but we have a large project where the structurals were off when overlaid in places by .75-1.5' in places (Most 95+% matched up perfectly) . Sometimes we are off by a few inches here and there but never this much. So yes we did catch it but the structural engineer is saying that none of that matters and that the cads don't need to match. So that leaves people in the field wondering which footing/wall outline is the correct one.

As for cross-checking an engineers work if the trades miss something it is also still an engineer's fault as well for not drawing it correctly in the first place. It is also a really good way to reintroduce human error into the equation when everything is having to be redrawn for estimating/construction purposes. Wrong in cad right on paper isn't really a thing. When I do take-offs for things I use measurements to scale. If I pick a line that is 24.75 but it says 25 I then have the wrong scale and my estimates are wrong and I can't use any type of earthwork program to accurately dig footings.

 

[BUGGAR]

"As for cross-checking an engineers work if the trades miss something it is also still an engineer's fault as well for not drawing it correctly in the first place."

I Think I'll not share with you.

 

[EngineeringEric]

I will say it is my fault if i dimension that beam as 24.75' but if i tell you it is 25' and you buy a beam only 24.75' because you scaled.... that your fault. Do engineers still need to say "Do not scale off these drawings"?

But if i mislabel something, i do not pawn that off on a trade. that is my fault and i hope the trade will notice it and RFI it.

 

[steellion]

"Do engineers still need to say "Do not scale off these drawings"?"

Yes.